1. Field of Invention
Exemplary aspects of the present invention relate to a nonvolatile semiconductor memory device, and a control method thereof.
2. Description of Related Art
As industrial development progresses, various types of nonvolatile semiconductor memory devices are being developed. One such related art device is a MONOS (Metal-Oxide-Nitride-Oxide-Semiconductor on substrate) type nonvolatile semiconductor memory device. See U.S. Pat. Nos. 6,044,022 and 6,081,456. In such a memory device, an electron trap region is formed between a gate electrode and a substrate in a memory chip. The amount of electrons in the trap region is controlled by electric-field control. Since the amount of electrons in the trap region is stored for a long time, the memory chip can be used as a nonvolatile memory.